1. Field of the Invention
This invention is directed to the catalytic alkylation of aromatic hydrocarbon molecules and is particularly concerned with a process for liquid-phase alkylation.
2. Description of the Prior Art
Alkylation is one of the most important and useful reactions of hydrocarbons. Lewis and Bronsted acids, including a variety of natural and synthetic zeolites, have been used as catalysts. Alkylation of aromatic hydrocarbon compounds employing certain crystalline zeolite catalysts is known in the art. For instance, U.S. Pat. No. 3,251,897 describes liquid phase alkylation in the presence of crystalline aluminosilicates such as faujasite, heulandite, clinoptilolite, mordenite, dachiardite, zeolite X and zeolite Y. The temperature of such alkylation procedure does not exceed 600.degree. F., thereby maintaining patentee's preferable operating phase as substantially liquid.
Also, U.S. Pat. No. 2,904,607 shows alkylation of hydrocarbon compounds in the presence of certain crystalline zeolites. The zeolites described for use in this patent are crystalline metallic aluminosilicates, such as, for example, magnesium aluminosilicate.
U.S. Pat. Nos. 3,631,120 and 3,641,177 describe liquid phase processes for alkylation of aromatic hydrocarbons with olefins in the presence of certain zeolites. U.S. Pat. No. 3,631,120 discloses use of an ammonium exchanged, calcined zeolite having a silica to alumina mole ratio of between 4.0 and 4.9. U.S. Pat. No. 3,641,177 discloses use of a zeolite catalyst activated in a particular manner.
Unfortunately, when propylene and higher molecular weight olefins were used for alkylation in the presence of zeolite ZSM-5, side reactions such as dealkylation and so forth take place and usually significantly reduced the selectivity to desired products.
U.S. Pat. No. 3,755,483 disclosed that the vapor phase reaction of propylene with benzene and toluene, in the presence of zeolite ZSM-12, gave high activity and high selectivity to produce isopropylbenzene and isopropylmethylbenzene. However, the process necessitated operation in the vapor phase with relatively high temperatures and pressures, thereby promoting dealkylation and olefin decomposition which was especially evident when the alkylating agent comprised an olefin of three or more carbon atoms.